Revised 8 / 06 (Monroe 6th ed.)




General Statements (C.Y.A.)


Solar System lab exercise

Mechanics of the universe

Origin and formation of the Universe

Future of the Universe

Formation of the Solar System: the Nebular Hypothesis


Please refer to GeoMan's Astronomy pages for more information on the cosmos.


General Statements (C.Y.A.)

Books make many statements as though they are facts, as opposed to theories

It is true that the suppositions are often base on hard empirical data

Obtained using the Scientific Method

Need to be verifiable and reproducible

Much based on mathematical models which no normal mortal can hope to understand

"Figured out" by brilliant minds

Galileo, Newton, Einstein, Hawking, (Sagan?)

It's important to keep in mind that the processes discussed happened a long time ago, or a long way from here, or both

These represent theories based on current levels of understanding

There are no direct methods to observe the formational process of the universe

All methods are essentially indirect and involve some pretty major assumptions

So, let's keep the uncertainty factor in mind while we discuss the early formational period of the universe, the solar system, and the earth



Study of the sky has always fascinated humans

It's easy to do, and before electric lights and TV, it was ALMOST all there was to do at night

We're not going to spend a bunch of time on the history of astronomy

It is clear that many non-European cultures were highly advanced in some of their astronomical observations and interpretations

We tend to get hung up on European history at the expense of the rest of the world

In actuality, Europe during the Middle Ages was about as far behind as one could imagine

Scientists thought that the Earth was in the center (as well as being flat!) into the 1500's

Look into the sky and it is obvious that there are objects out there which emit energy

Over the ages we have become increasingly better in our ability to look into the sky

Currently: analyze the light and determine physical and compositional properties

In our immediate vicinity

Sun, 9 planets, and asteroid belt

In the distance

Countless stars & clusters


We're in the Milky Way galaxy

Spiral variety (there are several other types of galaxies)

100 billion stars minimum

Takes 250 million years to rotate

DIGRESS TO: Scientific notation

Definitely useful in astronomy!

Our sun is an 'average' star

Rather insignificant

Way out on a spiral arm - like Luke Skywalker's home planet

At night you can look out along plane of the galaxy and easily see the heart of the Milky Way

The "known" universe is truly immense

Estimate at least 3 X 1010 galaxies in universe

Islands of stars in the vast void of space

And still going (Hubble Deep Field)

Light speed (186,000 miles per second)

We look back in time as we look out into the universe

See it as it was, not as it is

Even the sun is 8 minutes old news!

Nearly impossible to detect other planetary systems

Planets are dark bodies - don't emit visible energy

However, they do have mass and therefore a gravitational effect on the star they orbit

Whoa! What's a Gravitational Effect

Drop book

Did the book fall down or pull the earth up?

Early workers were not sure

Newton's "Universal Law of Gravity": G=M1M2/D2

Explain with some examples

Introduce concept of critical mass

Jupiter is big, but not quite big enough to be a star

Called a "Dark Body"

This gravitational pull can affect the motion of the star (which we can measure)


Outside for lab exercise

How much matter are we talking about in our solar system?

Let's build a scale model of the solar system

Starting with the Sun as a 9" basketball
Planet             Size                 Distance
Mercury      .03"    (0.8 mm)        31'     (9.5 m)
Venus       .076"    (1.9 mm)        58'    (17.8 m)
Earth        .08"    (2.0 mm)        81'    (24.6 m)
Mars         .04"    (1.0 mm)       123'    (37.4 m)
Jupiter      .90"   (22.9 mm)       420'   (127.8 m)
Saturn       .76"   (19.3 mm)       770'   (234.4 m)
Uranus       .30"    (7.6 mm)      1550'   (471.3 m)
Neptune      .28"    (7.1 mm)      2420'   (738.6 m)
Pluto        .03"    (0.8 mm)      3180'   (969.0 m)

Alpha Centauri                    4000 miles! (6640 km)


Mechanics of the universe

This is where some of the heavy-duty laws of nature come into effect

Sir Issac Newton (1642-1727)

Law of Gravity - discussed above

Three Laws of Motion

1st Law: Inertia

"A body continues in its state of rest, or of uniform motion in a straight line, unless it is acted upon by a net external force"

2nd Law: Force = mass X acceleration

"When an unbalanced force acts on a body, the body will be accelerated"

3rd Law: Law of action and reaction

"For every action there is an equal and opposite reaction"

A single force cannot exist. Every force is accompanied by an equal and opposite force

Like good and bad, heaven & hell?

These work well for most of what we have to deal with

Where they start to break down is when we try to get too big or small, or try to go too fast

Too slow doesn't seem to be a problem

This is where Einstein contributed with his work in the early 1900's

No way I'm qualified to discuss his work

Relativity and SpaceTime

E=MC2: at sufficient speed, matter and energy are interchangeable

Stephen Hawking (and others) attempting to develop theories to unify quantum mechanics, classical physics (Newton), and relativity (Einstein) into a single unified theory (Grand Unified Theory, or GUT)

Attempt to define to origin of matter and time, as well as possible futures


Origin and formation of the Universe

DIGRESS TO: space vs. nothing

There are two possibilities

1) Everything always existed like it is today, and time has no beginning

2) The universe (and time) began at a specific moment, and has been evolving and changing ever since

Observation of space indicate that everything is moving away from everything else

DIGRESS TO: Redshift

Rapid expansion of all matter

Implies that all matter must have started at a common center

Interpretation suggest that "the entire universe was compressed into a single infinitely dense point"

This is where I start to have trouble - no one was there, and we're talking about things which we probably aren't sufficiently advanced to understand

Not saying they are wrong, just skeptical enough to keep an open mind

Anyway, according to the theory, this point exploded (kaBoom)

The Big Bang

Marks the beginning of the universe and the start of time

"no ordinary explosion"

"This explosion instantly created the universe. Matter, energy, space and even time came into existence with this single event."

Assume 15 to 18 billion years ago

A "year" is based on our planetary system and may not have much relevance elsewhere

Evolution of universe after the explosion has been pondered

100 billion degrees Celsius at moment of explosion

DIGRESS TO: Fahrenheit, Centigrade and Kelvin scales

Rapid expansion and cooling

Down to 10 billion degrees after 1st second!

Too hot for atoms or matter as we know it

"Universe consisted of a mixture of radiant energy, electrons, and extremely light particles called neutrinos. Protons and neutrons also began to form."

"After 1.5 minutes" the temperature had fallen to 1 billion degrees

Simple atomic nuclei began to form

Still too hot for atoms

Continued to expand and cool "for the next million years"

"When the temperature dropped to a few thousand degrees, atoms formed and, in a sense, the modern Universe was born."

"With time, matter collected into galaxies, and within the galaxies stars were born."

This covers a lot of ground!

Remember: any report on stuff like this is only a "progress report," not dogma

DIGRESS TO: What's inside the last particle?

What is the actual shape and boundaries of the universe?

The big bang indicates that it must be like a balloon, but...

Like a donut? An hourglass, Only 3 stars total?

The jury is still out on these and many other questions concerning the possible existence of reality


Future of the Universe

One of two possibilities

1) Forever-Expanding Cosmology (Open Universe Theory)

Not enough matter to overcome the initial velocities and cause gravitational collapse

The galaxies will continue to expand "forever"

All stars will eventually use up their fuel and burn out

Universe will then be cold and dead, forever

2) Oscillating Universe Cosmology (Closed Universe Theory)

The expansion will continue, and slow, until the overall gravitation attraction of the matter will cause the universe to reverse and collapse in upon itself

The Big Crunch (or Big Suck)

This could lead to a new Big Bang, and another universe in the future

Were there others in the past?

How long has this been going on, and how could we ever find out

Theoretical stuff like this is a lot like geology - mostly impossible to prove or disprove, so we are free to speculate all we want without fear of contradiction

Astronomers are attempting to calculate the total mass of the universe to see which is the most possible

"However, the measurements are uncertain and the final answer elusive."

Currently research indicates that there is not enough matter to cause gravitational collapse

Unless there is much more dark matter than previously assumed


Formation of the Solar System: the Nebular Hypothesis

Our sun is a very ordinary star located far out in an arm of a spiral galaxy

The Milky Way

Can be viewed "edge on" on a clear night

Our sun appears to be smaller than average

Surface temperature 7500 deg. C.

It is thought that the solar system formed by the condensation of a "nebula"

A nebula is a widely dispersed cloud of interstellar gas and dust

Slowly rotating in space

Very cold (-270 deg. C.)

Gravitation attraction caused this matter to condense

Condensation resulted in faster rotation

The Law of Conservation of Angular Momentum

Ex. - a spinning ice skater

And an increase in temperature

Most matter accumulated into the center to form the sun

At some point the amount of matter was enough to set off the nuclear reactions which cause stars to emit energy, but not right away

Protosun: warmer than space but not hot enough to begin a fusion reaction

DIGRESS TO: Fission vs. fusion

Anyway, "over the course of geologic time" enough matter came together to start the reaction

Concurrent with the formation of the sun, the planets were forming

The concentration of the planets along the plane of the ecliptic indicates a similar origin for the entire solar system

Both in a time sense as well as the method of formation

The initial rotational velocity of the nebula increased as the nebula condensed

This increased speed caused the nebula to flatten and extend into a disk-shaped form

The central core formed the sun, with the planets being formed by "local condensation" within the relatively narrow disk arms

Collapse of the nebula was accompanied by increased temperature

Up to 2000 deg. C. fairly fast as the initial nebula "quickly" contracted

This temperature would keep the material in the gaseous state, even with the elevated density

Contraction began to slow after the initial condensation "to the size of the orbit of Mercury"

This central protosun continued to contract and heat up

Ultimately condensed into the sun

The disk portion, "where matter was far less concentrated", began to cool

Aggregates of material coalesced into larger bodies called "planetesimals"

"Ranged in size from a few kilometers to about 100 kilometers in diameter"

How do they know this?

Anyway, these chunks came together under the influence of gravity to form the planets

How long did it take for the planets to accumulate

The initial condensation may have happened quickly, "perhaps within 10,000 years"

In addition, it's still going on!

Continued accumulation

Some say more than 200,000,000 impacts per day!

Majority are dust and other small particles which burn up in atmosphere

Some larger chunks still out there

Earth Approaching Asteroids

Tunguska, Meteor Crater, and others


Please refer to GeoMan's Astronomy pages for more information on the cosmos.


GeoMan's Home Page | RCC Index | High School Geology Index


You are GeoManiac number since April 1, 1997